A belt tensioning device for a belt drive flat commonly has a continuous belt and at least two belt pulleys, of which one can function as a drive and one can function as an output of the belt drive. Such belt drives are especially used on combustion engines of a motor vehicle for driving accessories, wherein a first belt pulley sits on the crankshaft of the combustion engine and drives the belt. Further belt pulleys are assigned to the accessories, like for example water pump, electric generator or air conditioning compressor, and are rotatingly driven by the belt drive. The accessories are usually configured as consumers, i.e. they are driven by the belt pulley of the crankshaft via the belt. A slack side of the belt is formed between the crankshaft and the accessory adjoining the crankshaft in circumferential direction of the belt, said adjoining accessory typically being a generator. To ensure a sufficient wrap of the belt around the belt pulley, the belt is pretensioned by a tensioning roller of the belt tensioning device.
From EP 2 573 423 A1 a belt tensioning device for a belt drive of the above named type is known. The belt tensioning device has a base body, on which a tensioning arm is pivotably supported. The belt tensioning device is formed such that the pivot axis of the tensioning arm is arranged in the mounted condition within the outer diameter of the belt pulley of the accessory.
The efforts for reducing the fuel consumption or for reducing the CO2-emission are accompanied by the requirement for reducing the weight of vehicle components. Furthermore, in the field for belt tensioning devices the approaches for reducing the weight have already been pursued.
From EP 0 659 249 B1 a belt tensioning device with a carrier element and a tensioning arm is known. The tensioning arm can be made from metal or plastics. The tensioning arm is pivotably supported on the carrier element. The carrier element can be a metal or plastic lid, a mounting plate or a bracket.
From WO 2006/105656 A1 a belt tensioner for a belt drive is known. The belt tensioner comprises an arm and a pivot bushing, around which the arm is pivotably supported. The arm is a plastic molded part. Fiber reinforced organic resin material is used as plastic material. As reinforcing material glass fibers, aramid fibers, carbon fibers, steel fibers or nano-particles can be used.
Especially in compactly constructed belt tensioners high rotational variations in the belt drive, which are caused by changing from engine operation to starter operation, lead to a high friction and corresponding thermal loading of the belt tensioner. High requirements concerning the dampening of the system in the starter operation are connected therewith.
From DE 2011 003 113 A1 a tensioning device is known with a roller and a tensioner for travelling and dampening a movement of the roller. The tensioner has a housing, in which a spring and if necessary a damper are arranged. A cooling body with several cooling ribs is provided on the outside of the housing.
From DE 10 2007 015 676 A1 a tensioning device with a housing and a tensioning lever with a rotatable tensioning roller is known. Between the housing and the tensioning lever a helical spring is effectively arranged. On an end of the spring, a brake shoe is arranged, which can be pushed against a cylindrical inner wall of the housing for a good heat transfer.
From DE 103 33 876 A1 a tensioning element is known with a belt pulley, which is rotatably supported by a rolling bearing on an attachment member, and with a spacer, on which the inner bearing race of the rolling bearing is arranged. The spacer is in thermal contact with the inner bearing race and is made from a material with good thermal conductivity.